The invention relates to a synthetic material that can be used as a wood substitute. In particular, the invention relates to a polymer/cellulose composition that can be moulded into a wood-like material.
Throughout history wood, or timber, has been one of the most abundantly utilised natural materials. Wood has served humankindxe2x80x94and continues to serve humankindxe2x80x94as a construction material, as a raw material for other materials such as paper, and as a fuel. Indeed, there is hardly a human activity where wood does not play some role.
Humankind""s utilisation of wood, coupled with destruction of forests, has resulted in a shortage or total lack of some types of wood. Continued utilisation will more than likely result in almost all wood being in short supply. Consequently, there is considerable emphasis on more efficient use of wood in construction. For example, rather than traditional processing of trees into lumber, it is now common to xe2x80x9cchipxe2x80x9d a whole tree, with the resulting chips being used to manufacture wood panels and the like. Wood panels manufactured from wood chips are commonly referred to as xe2x80x9cchip boardxe2x80x9d and require a binder to maintain the integrity of the panel.
A disadvantage of manufactured wood products such as chip board is that toxic fumes can be released when the material is burnt. Furthermore, not all manufactured wood products are readily biodegradable or biodegradation results in toxic residue.
It would therefore be desirable to have available a wood substitute that has substantially the same properties as natural wood in terms of strength and durability yet can be biodegraded without leaving toxic residues and combusted without emitting toxic fumes.
The object of the invention is to provide a wood substitute that retains the necessary properties of natural wood for construction purposes and which can be biodegraded to non toxic residue or can be combusted without emission of toxic fumes.
Other objects of the invention are to provide a composition for producing the wood substitute and to provide a process for producing the wood substitute.
In one embodiment, the invention provides a composition for forming a wood substitute, the composition comprising 30 to 70% (volume by volume) of a high molecular weight aliphatic polyester and the balance a comminuted cellulose-containing plant material, wherein said aliphatic polyester comprises 1,4-butanediol condensed with adipic acid and/or succinic acid.
In another embodiment, the invention provides a process for producing a wood substitute, the process comprising the steps of:
a) heating a composition comprising 30 to 70% (volume by volume) of a high molecular weight aliphatic polyester and the balance a comminuted cellulose-containing plant material at a temperature of 110 to 180xc2x0 C. to provide a flowable material, wherein said aliphatic polyester comprises 1,4-butanediol condensed with adipic acid and/or succinic acid;
b) forming said heated material from step (a) into a desired product; and
c) allowing said product to cool to at least ambient temperature.
In other embodiments of the invention, there are provided wood substitute products formed using the composition of the invention.
The present inventors have found that a material having all of the desirable properties of wood can be prepared from a composition comprising comminuted plant material in combination with particular high molecular weight aliphatic polyesters as a binder. Products formed from the composition are biodegradable and combustion does not give off toxic fumes.
A key component of the composition is the high molecular weight aliphatic polyester. By xe2x80x9chigh molecular weightxe2x80x9d, it is meant that the polyester has a number average molecular weight (Mn) of at least 5,000 and weight average molecular weight (Mw) of at least 30,000. Typically, the molecular weight (Mw) of the aliphatic polyester falls within the range of 40,000 to 300,000.
As indicated in the above definitions of embodiments of the invention, the aliphatic polyester comprises 1,4-butanediol and aliphatic dicarboxylic acids such as succinic acid and adipic acid. These polyesters and processes for their preparation are described in U.S. Pat. No. 5,310,782 and U.S. Pat. No. 5,436,056, the contents of which are incorporated herein by cross reference. The properties of the polyestersxe2x80x94including their biodegradabilityxe2x80x94are discussed in an article by Takashi Fujimaki published in Polymer Degradation and Stability, Vol. 59, pp. 209-214 (1998), the entire content of which is also incorporated herein by cross reference. The polyesters the subjects of the foregoing publications are manufactured by Showa Highpolymer Co., Ltd of Tokyo, Japan and are sold under the trade name xe2x80x9cBionollexe2x80x9d. Two series of polyesters are commercially available, these being a polybutylene succinate polyester coded #1000 series and a polybutylene succinate adipate copolymer coded #3000 series.
The cellulose-containing plant material of the composition according to the invention can be any suitable plant material including, but not limited to the epidermis and cortex of plants, and other material such as seed coat. Specific examples of suitable plant material are: nutshells such as pecan nutshells, peanut shells and the like, and other cellulose-containing waste material such as sugar cane bagasse.
The plant material is comminuted using any procedure known to those of skill in the art. The size of comminuted particles can range from a fine powder up to about 5 mm in size.
Compositions can include other additives for visual effect and weight minimisation. For example, compounds such as fly-ash, talc, pigments and the like can be added for visual effect while micro-balloons, hollow glass spheres, foaming agents and the like can be included in compositions for weight minimisation. The additives can comprise 2 to 5% of the volume of the final composition without affecting biodegradability.
In one application, the wood substitute is used as a plant container such as a seedling tray or pot plant. In this application, the wood substitute composition can be combined with plant growth compounds (either synthetic or natural) and/or plant fibre. Plant containers made from the wood substitute composition of the invention have the advantage that they are rigid like plastic plant containers yet are readily biodegradable. They are also suitable for automated planting.
Blending of the aliphatic polyester and the comminuted plant material can be done using any suitable method. For example, the raw polymer, the comminuted plant material, and any other additives, can be blended using a twin screw extruder. The extrusion process is typically carried out over a temperature range of 160 to 240xc2x0 C. in which range the polyester is liquified. The molten output of the extruder can then be compacted and formed into convenient volumes for formation into wood substitute articles.
Alternatively, the wood substitute composition can be prepared by pregrinding the polyester materialxe2x80x94which is typically available as pelletsxe2x80x94by a cryogenic process using liquid nitrogen. The powdered polyester can then be combined with the comminuted plant material and any other additives using a machine suitable for mixing dry materials. After mixing the composition so formed can be divided into suitable volumes for ultimate use in preparing wood substitute articles.
Compositions according to the first embodiment defined above can be stored prior to processing into a wood substitute product provided that storage is in a desiccated atmosphere.
In the process of producing the wood substitute, the compositionxe2x80x94which can be considered to be similar to a thermosetting plastics materialxe2x80x94is heated sufficiently to give a polymeric whole. The formation step of the process described above, step (b), can be by any of the methods known to those of skill in the art. For example, compression, vacuum, injection, extrusion or rotation moulding can be used to form the product. The product can also be a sheet for subsequent form moulding or can be powdered for subsequent rotation moulding.
The cooling in step (c) of the process can be to less than ambient temperature if desired. In such an instance, cooling is mechanically aided. Mechanically aided cooling can also be applied to rapidly lower the temperature of the product to ambient or lower as desired.
The wood substitute product of the invention can be used to form articles normally made of wood such as furniture components, architectural mouldings, building construction elements including panels, decorative articles, and household or office articles such as ash trays, storage containers, trays and the like. The wood substitute can be formed by an extrusion process into sheets of corrugated material suitable for packaging. Such panels or solid panels of the wood substitute can also be used for formwork in building construction.
The wood substitute is particularly suited for the production of funerary articles such as coffins or caskets, urns, wall plaques and coffin ornaments. The suitability of the material for the production of funerary articles lies in it being readily biodegradable and combustible without emission of toxic fumes.
Having broadly described the invention, non-limiting examples of compositions and application of the process will now be provided.